Now you see it: The holy grail of metamaterials has become the kind of invisibility shield that has fired the human imagination from H.G. Wells' Invisible Man to the adventures of Harry Potter.

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PARIS: The age-old fantasy of rendering objects invisible took a sharp step toward reality Sunday when scientists said they had created a material that can bend visible light in three dimensions.

For now the vanishing act takes place on a nanoscale, measured in billionths of a metre. But there is no fundamental reason why the same principles can't be scaled up one day to make invisibility cloaks big enough to hide a person, a tank or something bigger, the scientists say.

Advances in metamaterials

The groundbreaking experiments, led by Xiang Zhang at the University of California in Berkeley and the Lawrence Berkeley National Laboratory, both in the U.S., are reported simultaneously in the British journal Nature and the U.S. journal Science.

Recent advances have created other so-called metamaterials – artificially engineered structures with optical properties that bend light in unnatural ways.
But previous attempts had two severe limitations.
One was that they only worked on the microwave range of the light spectrum, bending wavelengths much too long to be visible to the human eye.

The second was that – up to now – it only worked on flat, two-dimensional systems (see, Invisibility cloak unveiled, Cosmos Online).

The new material, by contrast, produces what is known as a "negative refractive index" needed to make an invisibility cloak within a visible light spectrum and in three dimensions.

Negative refraction – or "left-handed" – materials deflect light in a way which is contrary to the normal "right-handed" rules of electromagnetism.

The light travels in the opposite direction that it normally would when passing from one material to another, such as from air through water or glass.

One possible application would be the construction of special lenses for optical microscopes that could focus on things as tiny as molecules.

Ultimate camouflage

But the holy grail of metamaterials has become the kind of invisibility shield that has fire the human imagination from H.G. Wells' Invisible Man to the adventures of Harry Potter.

The military, which funded the research, is especially keen to develop materials that could usher in an entire new generation of stealth technology (see, Coming soon: cloaked submarines, Cosmos Online).

The metamaterial developed by Zhang and his colleagues has a multi-layered 'fishnet' structure composed of alternating layers of silver and magnesium fluoride, which is transparent over an extremely wide range of light wavelengths.

"In the case of invisibility cloaks or shields, the material would need to curve light waves completely around the object like a river flowing around a rock," Zhang told the U.K.'s Sunday Times newspaper.

"An observer looking at the cloaked object would then see light from behind it, making it seem to disappear," he said.